# Static Friction of a washing machine

#### brayrbob

Here is my problem,
A washing machine has a weight of 975 N. It requires a minimum force of 350 N to move it along a tile floor. What is the coefficient of static friction between the washing machine and the tile floor?

This is the equation I used to find the coefficient of static friction
us = mhg/mbg This isn't written right, but I don't know how to write the equations with the dropped letters.

us = 350/975 = .359 Now I'm just wanting to see if I've done this correctly.

This is my first course in physics ever, and am having trouble understanding everything.

Thanks,
brayrbob

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#### FredGarvin

The normal force is 975 N. The minimum force needed to push the machine is really the same as the force due to friction (static). Therefore, use the basic equation for frictional force to solve for mu:

$$F_f = \mu_s F_N$$

where:
$$F_f$$ = Force due to friction
$$\mu_s$$ = Coefficient of static friction
$$F_N$$ = Normal force exerted by the object

$$350 N = \mu_s 975 N$$

$$\mu_s = .36$$

#### mukundpa

Homework Helper
Brayrbob
Do you mean 'minimum horizontal force' or simply 'minimum force', may be in any direction?

#### brayrbob

On that equation the answer is basically the same that I got except I forgot to round my decimal. Why would I have to use the friction force equation when I need to solve for the coefficient of static friction?

#### FredGarvin

brayrbob said:
On that equation the answer is basically the same that I got except I forgot to round my decimal. Why would I have to use the friction force equation when I need to solve for the coefficient of static friction?
I'm not quite following your question here. You have two knowns and one unknown. The equation used relates the three items directly. Why not use it?

#### brayrbob

The question just asks for minimum force.
I asked the question about which formula to use because my physics instructor gave us serveral formulas and since I'm supposed to solve for the coefficient of static friction, I just want to be sure I use the right formula.

#### zwtipp05

brayrbob said:
On that equation the answer is basically the same that I got except I forgot to round my decimal. Why would I have to use the friction force equation when I need to solve for the coefficient of static friction?
The "minimum force required to move an object" is basically the same thing as saying "the force need to overcome friction and move the object". It's just a bit easier to say

#### mukundpa

Homework Helper
The minimum force required to move an object on a surface depends on the angle at which the force applied to pull the object. If it is not stated that the force is applied horizontally then the answer will be different. The component of the force applied in vertical direction will change the normal reaction and hence the limiting friction force.

The angle, at which the body should be pulled, with force to be minimum, should be tan^-1(u), where u is coefficient of friction.

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